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From: john@frog.UUCP (John Woods, Software)
Newsgroups: comp.lang.c
Subject: Re: asm statements & the stack
Message-ID: <1666@frog.UUCP>
Date: Thu, 15-Oct-87 15:59:00 EDT
Article-I.D.: frog.1666
Posted: Thu Oct 15 15:59:00 1987
Date-Received: Sat, 17-Oct-87 09:26:43 EDT
References: <110@teletron.UUCP>
Organization: Superfrog Heaven [ CRDS, Framingham MA ]
Lines: 42

In article <110@teletron.UUCP>, andrew@teletron.UUCP (Andrew Scott) writes:
> 
> Many C compilers have one variation or another on the asm() "function"...
> What can I do in an asm() statement?

"Nothing."

> The question arises because I was
> bitten by the compiler's code generation method.

That's where the answer comes from.

> I was writing a function which must be non-interruptable. ...
> Should I be angry with the compiler writer...?
No.

The only solution you can believe in is to use function calls to assembly
modules.  This way, you can (A) know that it really works for real, not by
accident, (B) change the compiler at will (next release of the same one, or
a new compiler altogether -- which would basically chuck your old asm()s out
the window, most likely, and SOME compilers do not permit asm statements
at all (some don't even have an assembly language intermediate stage)),
and (C) change to a new processor type with less effort (the assembly
code is localized in one module).  If your time-critical routine cannot deal
with wasting 72 clock cycles on subroutine linkage (5.76 microseconds at
12.5Mc, plus wait states), then you probably ought to write the whole routine
in assembly, because the C compiler is probably wasting more than that on
other little bobbles.

"Pluck the millisecond-wasting bad algorithms from thine own mind before
complaining about the micro-second wasting nature of high-level languages."

Or something like that.

--
John Woods, Charles River Data Systems, Framingham MA, (617) 626-1101
...!decvax!frog!john, ...!mit-eddie!jfw, jfw@eddie.mit.edu

"Cutting the space budget really restores my faith in humanity.  It
eliminates dreams, goals, and ideals and lets us get straight to the
business of hate, debauchery, and self-annihilation."
		-- Johnny Hart